We will hold on to the check until after you check-out. Though we usually rely on our guests' reports, it is impossible to determine if there was any damage done until we have cleaned the apartment and checked for anomalies.
Luckily for us, we have NEVER had to cash in a security check in the past and we normally destroy it after our guests leave. Only a few guests have asked us to return their checks by mail in the past. If such is your request, then we are happy to oblige. Just make sure you provide us with a return address.